Tanning with tris(hydroxymethyl)nitromethane and a polyhydric phenol

ABSTRACT

A process for tanning skins in which skins are first impregnated and drummed at a pH range of 4.5 to 4.7 in a buffered aqueous solution containing tris(hydroxymethyl)nitromethane and a polyhydric phenol such as resorcinol, catechol, hydroquinone, pyrogallol and phloroglucinol. During the operation the pH of the tanning solution is adjusted to the range of 8.0 to 8.5 and the skins drummed until tanned. Skins tanned by the above process can be retanned with any other tanning material.

United States Patent Wallace Windus Meadowbrook;

Muriel L. Happich, Jenkintown, Pa.; John S. Showell, Washington, D.C.

Jan. 8, 1970 Nov. 2, 197 l The United States of America as represented by the Secretary of Agriculture Inventors Appl. No. Filed Patented Assignee TANNING WITH TRISGIYDROXYMETHYL) NITROMETHANE AND A POLYHYDRIC PHENOL 11 Claims, No Drawings Primary Examiner-George F. Lesmes Assismn! E.raminer-B. Bettis Anorneyx-R. Hoffman and W, Bier ABSTRACT: A process for tanning skins in which skins are first impregnated and drummed at a pH range of4.5 to 4.7 in a buffered aqueous solution containing tris(hydroxymethyhnitromethane and a polyhydric phenol such as resorcinol, catechol, hydroquinone, pyrogallol and phloroglucinolv During the operation the pH of the tanning solution is adjusted to the range of 8.0 to 8.5 and the skins drummed until tanned. Skins tanned by the above process can be retanned with any other tanning material.

TANNING WITH TR1S(HYDROXYMETHYIJNITROMETHANE AND A POLYHYDRIC PHENOL A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to the tanning of skins and hides. More particularly, it relates to a new in situ tanning-process using tris(hydroxymethyl)nitromethane [2-(hydroxymethyl)- 2-nitro-1,3-propanediol] hereafter referred to as THNM, and free phenols under controlled conditions.

THNM by itself is a very poor tanning agent and cannot be used to produce an acceptable leather. Free and initially uncombined phenols are also very limited in tanning applications. In fact, many phenols such as resorcinol have no tanning ability per se. Even mixtures of phenols and aldehydes are not generally applicable as combination tannage agents. Fo'r'instance, of the dihydric phenols, the orthoand paraderivatives, catechol and hydroquinone, exhibited no tanning power when combined with formaldehyde. Although the meta derivative, resorcinol, gave a satisfactory tannage, the leathers were unstable to light and darkened with ageing even in 'the absence of light.

Since THNM and resorcinol are both extremely poor tanning agents, it was highly unexpected that the combination would be useful in a process to produce high quality leather. Sheepskins tanned with THNM at pH levels of about 1.5, 4.5 and 8.0 to 8.6 hadthe appearance and feel of raw skin. The highest shrinkage temperature was obtained after 8 days of tanning at 64 C. and at a pH of 8 .0 to 8.6. Addition of resorcinol and further tannage for 24 hours produceda soft, flexible well filled leather having a shrinkage temperature'of92" C.

One object of the present invention is to provide a process for making good quality leather, one that is full and mellow,

with good temper, strength and appearance and one that is saleable.

Another object is to produce a leather having perspiration to be tanned is impregnated with an aqueous solution buffered to a pH range of4.5 to 4.7 and containing tris(hydroxymethyl) nitromethane and a polyhydric phenol and then adjusting the pH ofthe tanning solution to and maintaining it at about 8.0 to 8.5 until the skin, hide or collagen is tanned.

The adjustment of the pH of the tanningliquor is an essential feature of the process. Maintenance of the tanning liquor at an acid pH for the entire process as shown in examples 4 and 5 as set forth later resulted in only partial utilization of the tanning agents. At a pH level of 4.5 or below very little tanning took place and a hide or skin so treated had the appearance of raw hide or skin and showed no appreciable change in shrinkage temperature. Maintenance of the tanning liquor at a pH of about 6.7 for the entire process resulted in a fla't and tinny leather having a shrinkage temperature of about 74-77 C.

Tanning by the process of this invention consistently produces a strong, soft, mellow, good appearing leather with a shrinkage temperature of between 85 and 95 C. Although the ratio of THNM to phenol can vary over a substantial range, a one to one ratiois preferred.

Hides, skins or collagen tanned by the process of this invention can be retanned with any other tanning material. Leather tanned by the process of this invention has been retanned with basic chromium sulfate, with glutaraldehyde and with vegetable tannins consisting of chestnut, bisulfited quebracho and wattle. All retannages have produced high-quality leathers.

The process of this invention differs from the prior art in that the activity of the tris(hydroxymethyl)nitromethane depends upon electron withdrawal by the nitro group. This is the first time that electron withdrawal has been used to activate a molecu le'to react with'resorcinol in dilute aqueous solution at room temperature to produce tanning molecules.

This invention is exemplified by the following experimental data:

EXAMPLES l-3 Each of three 50.0 g. samples of pickled lran sheepskin was placed in an individual tanning solution containing the following components: water, 100.0 g.; sodiumsulfate (anhydrous) 10.0 g.; sodium acetate, 1.5 g.; THNM, 5.0 g. After tumbling for 1.5 hours the pH of each solution was in the range of 4.5 to 4:6. su flicientH sO, was-then added to example 1 and suffic1entNa,CO was added'to' example 3 to adjust the pH of each solution to 1.7 and 8.5, respectively. The thi'ee skin samples in their respective tanning solutions at the above pH levels were then tumbled continuously for a total time of about 9 days. Each skin was then sampled and shrinkage temperature determined. The shrinkage temperatures foreach skin was as follows: example 1, 43 C.; e'xample'2, 56 C.; example 3, 65 C. None of the examples had the appearance or feel of a tanned skin.

At this stage 3.6 g. of resorcinol was added to each solution and the skins were given a final tumbling for about 1 more day. Sh'rinkage'temperatures were then determined to: be as follows: example 1, 41C.; example 2, 57 C.; and example 3, C.

Example 3 which was beige colored at this stage was removed from the tanning solution and treated as follows: washed with water, immersed in a solution acidified with an amount of H 80, adequate to adjust the pH of the skin to 4.0, removed from the acid solution, washed again with water to remove excess acid, fatliquored with a mixture of l .5 g. raw neatsfoot oil and 3.0 g. sulfated neatsfoot'oil and then dried. The dried leather was a good quality leather, full, soft, supple and mellow and'h'ad a shrinkage temperature of C.

Examples 1 and 2 were tumbled one additional day, removed from their respective tanning solutions and tre'ated in the manner described for example 3. The results in both'cases' EXAMPLES 4-7 Each of four5 0.0 g. samples of pickled lran sheepskin was placed 1n an individual tanning solutioncontainingthe following components: water, 100.0 g.; sodium sulfate (anhydrous), 10.0 g.; sodium acetate, 1.5 g.; THNM, 5.0 g.; resorcinol, 3.6 g. After tumbling for 1.5 hours, the pH of each solution was in the range of 4:6 to 4.7. Sufficient H580, was then added to example 4 and sufficient m co, was added to exampleso and 7 to adjust'the pH of each solution to 1.7, 7.1 and 8.0, respectively, after which the samples were tumbled for about 24 hours. The pH of each solution at this point'was as follows: example 4, 1.7.; example 5, 4.7; example 6, 7.3; and example 7,

8.0. Each skin waa then removed from the tanning solution were dried and the shrinkage temperature of each determined to be as followsz-exarnple 4, 56 C.; example 5, 59 C., example 6, 79; C., example 7, 88 C. Example 7 was soft and full and the best leather. Example 6 was not as soft and full as example 7 and had a light beige color. Examples 4 and Shada parchment like appearance and resembled dried raw skin.

EXAMPLE 8 A 50 g. sample of pickled lran sheepskin was placed in a tanning solution containing the following components: water, l g.; sodium sulfate (anhydrous), 10.0 g.; sodium acetate g.; THNM, 5.0 g.; resorcinol, 3.6 g. After tumbling for 1.5 hours the pH of the solution was 4.6. Then 1.0 g. of anhydrous sodium carbonate was added and drumming continued for two hours after which the pH was 7.1. An additional 0.5 g. of anhydrous sodium carbonate was added and the drumming continued for about 24 hours. The pH was then 7.9. The skin was removed from the tanning solution, washed, acidified to a pH of about 4.0, washed again and fatliquored. The dried leather was full, mellow, soft and strong. The shrinkage temperature of the finished leather was 84 C.

EXAMPLE 9 A 50 g. sample of pickled lran sheepskin was placed in a tanning solution the same as used in example 8 and treated in a similar manner except that after tumbling for 1.5 hours, only one addition of 4.0 g. of sodium carbonate (anhydrous) was made to raise the pH from 4.6 to 8.0. The leather obtained was strong, soft, mellow and full and had a shrinkage temperature of 86 C.

' EXAMPLE 10 A 50 gram sample of pickled lran sheepskin was placed in a tanning solution containing the following components: water, 100 g.; sodium sulfate (anhydrous), 10.0 g.; sodium acetate 1.5 g.; THNM, l0.0 g.; and resorcinol, 7.2 g. After tumbling for L5 hours the pH was 4.6. Enough sodium carbonate (anhydrous) was added in two separate portions to raise the pH to 8.0 and tumbling was continued for about another 24 hours. The sample was removed from the tanning solution and then acidified to about a pH of 4.0, washed again, fatliquored and dried. The dried leather had a shrinkage temperature of 84 C. and was strong, soft, mellow and full.

EXAMPLE I 1 A 50 gram sample of pickled lran sheepskin was placed in a tanning solution containing the following components: water, 100 g.; sodium sulfate (anhydrous) 10.0 g.; sodium acetate, 1.5 g.; THNM, 1.25 g.; and resorcinol, 0.9 g. After tumbling for 1.5 hours the pH was 4.7. Enough sodium carbonate (anhydrous) was added in one portion to raise the pH to 8.0 and tumbling was continued for about another 24 hours. The sample was removed from the tanning solution and then washed, acidified to about pH 4.0, washed again, fatliquored and dried. The dried leather had a shrinkage temperature of 83 C. and was strong and of good quality, but was not quite as full as skins tanned with larger amounts ofTHNM and resorcinol.

EXAMPLE l2 Three pickled cabretta skins, 1,230 g. wet, drained weight, were tanned in a small laboratory drum at about 75 to 80 F. using the following solution: water, 2,460 g.; sodium sulfate (anhydrous), 246 g.; sodium acetate, 37 g.; THNM, 123 g.; and resorcinal 37 esorcinol, 88 g. The skins were drummed 1.5 hours at pH 4.6. Forty-nine grams (4%) of anhydrous sodium carbonate was added and the drumming continued at a pH of 8.3. After 7.5 hours of tannage the shrink temperature was 88 C. Drumming was continued overnight for a total tanning time of24 hours. The final pH was 8.3 and the shrink temperature was 93 C. The skins were washed, acidified to a pH of4.0 with H SO,, washed again, wrung, fatliquored and processed into finished leather in a tannery. A good quality leather was obtained.

EXAMPLE 13 Three pickled cabretta skins, 1,435 g. wet, drained weight, were tanned in a small laboratory drum at about 80 to 85 F.

using the following solution: water, 2,870 g.; sodium sulfate (anhydrous), 287 g.; sodium acetate, 43 g.; THNM, 144 g.; and resorcinol, 103 g. After drumming for 30 minutes, the pH was 4.7. Twenty-nine grams of anhydrous sodium carbonate was added and the skins drummed for an additional hour. The pH was now 6.7. Fifteen grams of anhydrous sodium carbonate was added raising the pH to 8.3 and the skins were drummed again for a total tanning time of 7.5 hours after which the shrinkage temperature of the skins was 91 C. The skins were washed and drained overnight and then acidified to a pH of 4.0 with H washed again, wrung, fatliquored and processed into finished leather. A good quality leather was obtained.

EXAMPLE l4 Three pickled domestic sheepskins, 2,790 g. wet, drained weight, were tanned in a small laboratory drum at about 80 F. using the following solution: water, 5,580 g.; sodium sulfate (anhydrous), 558 g.; sodium acetate, 84 g.; THNM, 279 g.; and resorcinol, 199 g. The skins were drummed for 1.5 hours at a pH of 4.6. One hundred twenty-six grams of Na,co,H,o was added, the skins were again drummed until the total tanning time was 24 hours. At this time the pH was 8.2 and the shrinkage temperature of the leather was 89 to 91 C. The skins were then washed, acidified to pH 3.9 with H SO.,, washed again, fatliquored, paste dried and finished for shoe lining leather in a tannery. The leather finished well as shoe lining leather and the temper, appearance and tensile strength were adequate for this use as judged by a tanner.

EXAMPLES l5 and l6 Two fifty gram samples of Iran sheepskin, drained pickled weight, were tanned in solutions containing g. water, [0 g. sodium sulfate (anhydrous), 1.5 g. of sodium acetate, 5.0 g. THNM and 3.6 g. of a phenol, catechol in example l5 and hydroquinone in example 16. Each sample was drummed in its respective solution for about 1.5 at a pH of4.5 to 4.7. Sodium carbonate was added to adjust the pH to about 8.0 and drumming was continued for a total tanning time of 24 hours. The shrinkage temperatures were 78 C. and 80 C. respectively. Each skin was washed, acidified to pH 4.0 with H 80 washed again, fatliquored and dried. Satisfactory leather was obtained in each case.

EXAMPLES l7 and 18 Two fifty gram samples of lran sheepskin, drained pickled weight, were tanned in solutions containing I00 g. water (example l7) or g. water (example l8). 10 grams of sodium sulfate (anhydrous), 1.5 g. of sodium acetate, 5.0 g. of THNM and 4.2 g. of a phenol, pyrogallol in example l7 and phloroglucinol in example 18. Each sample was drummed in its respective solution for about 1.5 hours at a pH of4.6. Sodium carbonate was added to adjust the pH to about 8.0 and drumming continued for a total tanning time of 24 hours. The shrinkage temperatures of the leathers were 89 C. and 92 C. respectively. Each skin was washed, acidified to pH about 4.0 with H SO washed again, fatliquored and dried. Satisfactory leather was obtained in each case.

EXAMPLE 19 A sample of pickled cattlehide belly, 100 g. drained, wet weight was tanned in the following solution: 200 g. water. 20 g. of sodium sulfate (anhydrous), 3.0 g. of sodium acetate, 10 g. of THNM and 7.2 g. of resorcinol. The solution was drummed for 6 hours at a pH of 4.6. Enough sodium carbonate was added to raise the pH to 5.4 and drumming was continued for about 17 hours. The pH was then adjusted to 6.9 with sodium carbonate and the drumming continued for about another 6 hours. The pH was again raised to 7.5 and the drumming continued for about another 24 hours. The shrinkage temperature was 88 C. The sample was then allowed to soak in the tanning solution for about 64 hours at the end of which time the pH was about 7.4 and the shrinkage temperature was 93 C. The tanning solution was then adjusted to pH 4.0 with H 80 after which the shrinkage temperature was 95 C. The hide was washed with water, fatliquored and dried. Satisfactory leather was obtained. The tannage had completely penetrated and tanned the hide to make a soft, flexible fullthickness leather.

We claim:

1. A process for tanning skins comprising impregnating and drumming skins with an aqueous solution buffered to a pH in the range of 4.5 to 4.7 containing tris(hydroxymethyl)nitromethane and a polyhydric phenol, and adjusting the pH of the solution during the tanning operationto and maintaining it in the range of about 8.0 to 8.5 until the skins were tanned.

2. The process of claim 1 in which the polyhydric phenol is resorcinol.

3. The process of claim 1 in which the polyhydric phenol is catechol.

4. The process of claim I in which the polyhydric phenol is hydroquinone.

5. The process of claim 1 in which the polyhydric phenol is pyrogallol.

6. The process of claim 1 in which the polyhydric phenol is phloroglucinol.

7. A process for tanning skins comprising impregnating and drumming skins for about 1.5 hours with an aqueous solution buffered to a pH in the range of 4.5 to 4.7 containing tris(hydroxymethyl)nitromethane and a polyhydric phenol, adjusting the pH of the solution to a range of about 6.5 to 7.0, drumming the skins at this pH level for about I hour, readjusting the pH of the solution to a range of about 8.0 to 8.5 and drumming the skins at this pH level until said skins are tanned.

8. A process for tanning skins comprising impregnating and drumming skins with an aqueous solution buffered to a pH in the range of 4.5 to 4.7 containing tris(hydroxymethyl)nitromethane and a polyhydric phenol, adjusting the pH of the solution during the tanning operation to and maintaining it in the range of about 8.0 to 8.5 until the skins are tanned and then retanning said tanned skin with a second tanning agent.

9. The process of claim 8 in which the second tanning agent is basic chromium sulfate.

10. The process of claim 8 in which the second tanning agent is glutaraldehyde.

11. The process of claim 8 in which the second tanning agent is a blend of vegetable tannins consisting of chestnut, bisulfited quebracho and wattle. 

2. The process of claim 1 in which the polyhydric phenol is resorcinol.
 3. The process of claim 1 in which the polyhydric phenol is catechol.
 4. The process of claim 1 in which the polyhydric phenol is hydroquinone.
 5. The process of claim 1 in which the polyhydric phenol is pyrogallol.
 6. The process of claim 1 in which the polyhydric phenol is phloroglucinol.
 7. A process for tanning skins comprising impregnating and drumming skins for about 1.5 hours with an aqueous Solution buffered to a pH in the range of 4.5 to 4.7 containing tris(hydroxymethyl)nitromethane and a polyhydric phenol, adjusting the pH of the solution to a range of about 6.5 to 7.0, drumming the skins at this pH level for about 1 hour, readjusting the pH of the solution to a range of about 8.0 to 8.5 and drumming the skins at this pH level until said skins are tanned.
 8. A process for tanning skins comprising impregnating and drumming skins with an aqueous solution buffered to a pH in the range of 4.5 to 4.7 containing tris(hydroxymethyl)nitromethane and a polyhydric phenol, adjusting the pH of the solution during the tanning operation to and maintaining it in the range of about 8.0 to 8.5 until the skins are tanned and then retanning said tanned skin with a second tanning agent.
 9. The process of claim 8 in which the second tanning agent is basic chromium sulfate.
 10. The process of claim 8 in which the second tanning agent is glutaraldehyde.
 11. The process of claim 8 in which the second tanning agent is a blend of vegetable tannins consisting of chestnut, bisulfited quebracho and wattle. 